Electrical relaxation oscillator



Aug' 26, 1947-' P. K.. CHATTERJEA ET A1. 2,426,179

ELECTRICAL RELAXATION 'OSCILLATORSL Filed June l0, 1945 VOL T5 'A rms, C

Patented Aug. 26, 1947 l assignments, to International Standard`I lgllecy.tric Corporation, New York, N. Y., a corporal*tion of Delaware "`App1ie`atienlune 10, 1943;'.s'e1-iaLNo.' 490,284

In Great-Britain June 19, 1942 Eilie present invention relates to electricalrelaxation oscillators, and is directed towards eliminating "the distortion of the vvaves gener atedby the use oithermally sensitive resistance L devices known as tnermistors. l. .lhefmiStQrshaS/.e been ,in use for some .years and fare halatersed 4 hva temperature cofecient Lof resistance which maybe either positive ll -or negative and which :is moreover many times @the Corresponding cecentior `a pure! metal such as copper. This propertyrenders thermis- Etors particularly suitable. .for a Variety of special iapplicationsin eletriqcircuits.

Various different; materialsfale availableA for. 15

the--resistanceelementofiathermistor, these varz.i0 u s,matera1.s-hai/ine different 'properties in tether respects; asworie. example,Y av resistance material; `having abighlnegativetemperature co-efga-nes xide andnickel oxide,With `or Without itlfle.-` idition of, certanpther metallic oxides, the

11e-.being suitably.. heat treated.

ermistors have been employed in, two difafercntxforms; sa), known as, a directly heated! ithermistorand comprising, a resistance .element `Loiythe ,thermally. sensitive... resistance material gprovidelA With A suitable lead-fout ,conductors or terminals, and.., b) known as Aan indirectly heat- ;ed thermistor comprising. the dementia) .Lpro--` .vided in addition with Ya heating coil electrically insulated from .the-elements A directly .heated thermistor is primarily intended to be controlled by the currentJNhch lowsthroil'gh it'and which Varies the temperatureand alsojthe resistance` i accordingly. Such a thermistor will also be effected by tle"teinperatureloiflits surroundings and maytherefore .be used .for thermostatic con- 'trol and Vlikepurposes 'withi ithout ldirect indirectijfiie'ateu trierinistr 'is' chiefly designed to be heated by a controliinggurrent which flows -ih,fqught1 1= heating @oil andlwhich win-usually, 'il' ent fromi tliegcur- @valso begsubiectbotlimofnthe, `y es of control apisntof resistancecomprises amixture of man- 2Q Jing Kthe curvature ot title scanni resistance elementf Vno"Aconstantl'b 'ecailse their e Y ndenser tlieoscil tilon re jeenjmeniyjsteinednecfease es thegehareggm creases @ricamata reid nijiing are @at 199,. 'mister for couplingwtln I stages toen amplifying stage, the' th 25 ing, adapted 'to (change its' resistancefpro essvehrough it. "Anil e the f ellliiymg, weiser! Q3 eed.

50 connected to the control grid of V2. A resistance 56 producing the saWR-tooth oscillations is one of 2,426,179 x V V lhe well known types, and the arrangements of Ithe amplifying valve V2 are typical and might be provided in other ways. The invention lies in the coupling arrangement between the two valves.

As already explained, the rate of Variation of potential across the condenser is not uniform, and decreases as the charge increases.

In Fig. 2, ABC represents the ideal form of a single saw-tooth oscillation. The abscissae represent time and the ordinates represent, for example, the voltage applied to the grid of valve V2 in Fig. 1. AB is the scanning stroke and is shown as a straight line. BC is the iiy-back stroke, and is substantially a straight line at right angles to the time axis.

Assuming for the moment that the thermistor is replaced by a constant resistance, the form of the oscillation actually obtained will be like APC, on account of the decrease in the charging rate of the condenser C1 as it becomes charged. Suppose, now that the thermistor is again connected in the circuit as shown in Fig. 1 and an undistorted saw-tooth wave is applied to the blocking condenser C3 instead of the distorted wave derived from the condenser C1, but having the same initial slope. Then the thermistor temperature will be higher at the end of the scanning stroke, near B, than at the beginning because the current is greater. If, therefore, it has a positive temperature co-eicient of resistance, its resistance will be higher at the end of the stroke than at the beginning, and the voltage applied to the grid of valve V2 will be greater. A wave like AQC will now be obtained, the point Q being higher than the point B. Thus, if the resistances R5 and R are chosen so that BQ=BP, then substantially the curve ABC will be obtained when the distorted waves from the condenser C1 are applied to the blocking condenser Cs; in other words the thermistor has corrected the distortion of the saw-tooth waves by suitably changing the output to input voltage ration of the potentiometer.

It will be evident that if it is desired to use a thermistor with a negative temperature coetcient of resistance, similar correction will be obtained by interchanging the thermistor and the resistance R5 as illustrated in Fig. 3.

If desired, a second constant resistance can be connected in parallel with the resistance R of the thermistor as illustrated in Fig. 4.

Fig. 1 shows only one of the known arrangements as an example of the application of the invention. It will be evident that the same principles may be applied to' other forms of relaxation oscillators which do not employ a gas discharge valve, for example.

What is claimed is:

1. Signal wave source comprising means for generating a saw tooth wave, means for translating said wave having input terminals and means for changing the shape of said saw tooth wave comprising a resistor and a temperature variable resistor, said resistor being in series with said generating means, means for coupling said temperature vvariable resistor to said generating means and means for coupling said input terminals to said temperature variable resistor,

said temperature variable resistor having a variable resistance which changes progressively in the same direction during each voltage rise of said voltage wave.

2. Oscillator means comprising means for charging a condenser and means for discharging said condenser to produce a saw tooth wave, means for amplifying said saw tooth wave having input and output terminals, means for correcting undesired curvature in said saw tooth wave comprising a linear resistor and a temperature variable resistor connected in series to form a potentiometer, means for connecting said potentiometer across said capacity and means for coupling said input terminals across an intermediate point and a second point on said potentiometer, said temperature variable resistor having a non-1inear resistance which changes its resistance progressively in the same direction during each voltage rise of said saw tooth wave.

3V. A device in accordance with claim 2 in which said intermediate point is the junction point of said linear resistor and said temperature variable resistor.

4. A device according to claim 2 in which said temperature variable resistor is connected across said input terminals, and said linear resistor is connected in series with said temperature variable resistor between said capacity and said temperature variable resistor, the temperature coefcient of resistance of said temperature variable resistor being positive. 5. A device according to claim 2 in which said linear resistor is connected across said input terminals and said temperature variable resistor is connected in series with said linear resistor between said capacity and said input terminals, the temperature coefficient of resistance of the temperature variable resistor being negative.

6. A device according to claim 2 further comprising a second linear resistor, connected in parallel with the temperature variable resistor.

'7. A device according to claim 2 in which the characteristics of the said temperature variable resistor are so chosen that the total change of resistance of said temperature variable resistor during a voltage rise of said saw tooth wave produces a total increase in the output to input voltagel ratio of said potentiometer substantially suflicienty to compensate for curvature of predetermined portions of the saw tooth wave produced by said oscillator means.

PRAFULLA KUMAR CHATTERJEA. 'DERMOTVMTN AMBROSE.

REFERENCES orrED The following references are of record in the iile of this patent: 

